Characterizing the dynamics of a physical structure, such as its vibrational modes, is one part of predicting the real-world behavior of the structure. In addition, monitoring these structural dynamics can provide insights into changes to the structure over time, such as the weakening of particular portions of the structure. These characterizations can be used, for example, to evaluate the stability and/or soundness of a structure, in order to ensure that the structure is safe for its users. These physical structures may include, but are not limited to, civil, mechanical, and aerospace structures.
The process of characterizing structural dynamics can be classified as experimental modal analysis or operational modal analysis, where an experimental modal analysis supplies a known input force to the structure, and operational mode analysis relies only on measured response data, without control over the input forces.
Both experimental and operational modal analyses typically require physically-attached wired or wireless sensors such as accelerometers for measuring the vibration of the structures. The sensors themselves can be costly, and installation and maintenance of these sensors can be time-consuming, especially for long-term applications (e.g., structural health monitoring on large civil structures) that require significant maintenance for cabling (e.g., for wired sensors) or periodic replacement of the energy supply (e.g., batteries for wireless sensors). In addition, these physical sensors can result in mass loading on lightweight structures such as aerospace structures, thereby changing the structural dynamics of systems that they are intended to measure. Moreover, these sensors are typically placed at a limited number of discrete locations, and therefore provide low spatial sensing resolution that may be insufficient for modal-based damage localization, or model correlation and updating for larger-scale structures, and may be insufficient for accurately correlating and updating finite element models of the structures.
Non-contact measurement methods such as scanning laser vibrometers can provide high-resolution sensing capacity without the mass-loading effect; however, they make sequential measurements that require considerable acquisition time and can be labor intensive to use when the sensing areas are large. In addition, scanning laser vibrometers are also relatively expensive.